In many state-of-the-art cathode ray tubes, such as those employed in television and allied display applications, technological advancement has resulted in the development of efficient compacted electron gun structures encompassed within small diametered envelope neck portions. The required operating voltages for the various elements comprising these guns are supplied via a plurality of hermetically sealed connective leads or pins traversing and protruding from the integral size-related closure portion. These pins, which are usually oriented in a pin-circle array adjacent to the sealed exhaust tubulation, evidence rather close inter-lead spacings because of the restrictive circumferential arrangement. Since high voltage differentials are existent between certain of the leads, it has been conventional practice to insulate especially the high voltage leads by surrounding them with the adhesive dielectric material utilized to adhere the tube base to the closure portion of the tube.
An exemplary tube base is one fabricated of a plastic material formed to have an axial hollow thimble-like crown portion dimensioned to protectively encompass the sealed tubulation. Extending outwardly from the crown portion, in a shelf-like manner normal thereto, is a flange portion having a diameter in keeping with that of the tube closure portion. This flange, which exhibits a perimetrical rim upon which the closure portion is seated, is traversed by a plurality of apertures arranged in a circular array to accommodate the protruding connective pins of the tube. A minor arcuate section of the flange, whereat the apertures accommodating the high voltage pins are located, evidences a discrete areal surface indentation or recess. It is within this recess that a major portion of the dielectric adhesive is deposited to achieve the requisite adherence of the base to the tube, while simultaneously effecting the desired insulation for the respective high voltage pins. Due to the compact dimensioning between the surface of the base flange and the adjacent closure surface, only a small amount of adhesive can be applied in the restricted spacing therebetween. Thus, the major base-to-tube adherence factor is achieved conjunctively by the limited area of indentation disposed adhesive and the interaction of the pins in the base apertures.
In usage, the base of the tube is mated with connective socket means associated with the respective image display device. It has been conventional practice to integrate adjustable portions of the tube control circuitry on a subchassis arrangement attached to the socket member into which the base of the tube is fitted. This associated circuitry adds mass to the socket component, which in turn subjects the base-to-tube adherence to twisting and/or pulling stresses. Since the tube proper is independently seated and securely affixed, and the base per se is snugly fitted within the receiving socket (which has flexible leads attached thereto), most stresses resulting from the socket mass are applied to the adhesive bond and pins; such being concentrated mainly in the interfacial region between the base and the tube closure portion. Weakening or failure of the limited deposition of adhesive sometimes allows the base to tilt or shift thereby subjecting the pins to deleterious bending strains resulting in fractures of one or more of the hermetic seals. Thus, the possibility of base-to-tube adherence failure is an important factor relating to the achievement of desired tube quality.